Techniques of mixing fibrous inorganic fillers with polyolefin resins in order to improve heat resistance and rigidity of the polyolefin resins have already been known, and utilized in many fields including automotive materials. Above all, molded articles obtained by adding glass fiber which is a fibrous inorganic fiber having thin fiber diameter and high aspect ratio to the polyolefin resins are attracting attention because they have high rigidity. However, the fiber-reinforced resins reinforced with the inorganic fillers like this pose problems of decreased impact resistance and discarding. In order to solve such problems, it has been tried to replace the fibrous in organic fillers such as glass fiber with organic fiber.
Patent document 1 discloses an organic fiber-containing resin composition composed of a polyolefin, organic fiber and inorganic fiber. It is described that a fiber-reinforced resin composition having high mechanical strength and elasticity and excellent in impact resistance can be obtained by combining the organic fiber and the inorganic fiber. However, the inorganic fiber is contained as described above, so that discarding thereof is difficult, and ash of the inorganic fiber remains after thermal recycle.
Patent document 2 and the like disclose a polyolefin resin composition obtained by biaxial kneading of a mixture of a polyolefin having a melting point of 170° C. or less and an inorganic filler with synthetic fiber having a melting point of 200° C. or more. It is described that according to this invention, impact strength and rigidity can be improved without decreasing dimensional stability, surface smoothness, rigidity and hardness, for example, by adding the tabular inorganic filler to the polyolefin, and thereafter, adding the organic fiber. However, the inorganic filler such as a hydroxide or inorganic filler is added, so that the problem of remaining ash still remains unsolved.
In order to solve these problems, various methods are disclosed. For example, patent document 3 discloses a technique of using organic fiber having a melting point 50° C. or more higher than that of a polyolefin resin as a reinforcing material, heating the polyolefin resin at a temperature 40° C. or more higher than the melting point thereof, and performing impregnation to the organic fiber within the range that the impregnation time does not exceed 6 seconds. It is described that thermal degradation of the reinforcing fiber does not occur and breakage thereof is also decreased, resulting in being able to obtain an excellent organic fiber-reinforced resin composition.
However, according to this method in which the organic fiber is merely immersed in a molten resin bath of the polyolefin resin and then pulled out, there have been problems of extremely low fiber dispersibility in the polyolefin resin, increased strength variation of a molded article associated with unevenly distributed fiber, and further, poor surface appearance of the molded article.
Further, patent document 4 discloses that a molded article which is strong and has high rigidity and good appearance is obtained by using organic fiber-reinforced resin pellets in which organic fiber has a melting point of 150° C. or more and 30° C. or more higher than the melting point of a resin composition, a monofilament fineness of 0.1 to 20 dtex and a total fineness of 2,000 to 700,000 dtex, and 65% or more of the total surface area of the organic fiber is in contact with the resin composition. The dispersion and the appearance of the molded article are improved thereby to some degree, but still insufficient. Furthermore, the fiber used requires the specified fineness, so that it has a limitation also in control of physical properties as an organic fiber composite material.
Patent document 5 discloses an organic fiber-reinforced resin using organic fiber which is surface treated with a bundling agent containing a nucleating agent having a nucleating function. However, even when this method is used, opening of the fiber is insufficient to cause poor dispersion. As a result, only a molded article having poor appearance is obtained.
Patent document 6 discloses a method of coating fiber surfaces with an acid-modified polyolefin resin or adding the acid-modified polyolefin resin into a polyolefin resin. However, even when this method is used, organic fiber dispersion is still insufficient, and breaking elongation also considerably decreases, although interface strength between the resin and the fiber increases.
Patent document 5 discloses an organic fiber-reinforced resin using organic fiber which is surface treated with a bundling material containing a nucleating agent having a nucleating function. However, even when this method is used, opening of the fiber is insufficient to cause poor dispersion. As a result, only a molded article having poor appearance is obtained.
Patent document 6 discloses a method of coating fiber surfaces with an acid-modified polyolefin resin or adding the acid-modified polyolefin resin into a polyolefin resin. However, even when this method is used, organic fiber dispersion is still insufficient, and breaking elongation also considerably decreases, although interface strength between the resin and the fiber increases.
Patent Document 1: JP-A-4-202545
Patent Document 2: JP-A-6-306216
Patent Document 3: Japanese Patent No. 3073988
Patent Document 4: JP-A-2005-040996
Patent Document 5: JP-A-2002-167518
Patent Document 6: Japanese Patent No. 2941320